Copper sulfate toxicity to two isolates of Ichthyophthirius multifiliis relative to alkalinity

Abstract

Theronts from 2 different strains of Ichthyophthirius multifiliis (AR1 and AR5) were exposed to copper sulfate (CuSO 4 ) in waters of different total alkalinities and observed for 4 h to determine relative toxicity and kinetics of parasite mortality. Consistent with the known solubility properties of the metal, Cu was significantly more toxic to cells maintained under low (48 mg l ) total alkalinity conditions. This was reflected in both the median lethal concentration (LC 50 ) values and rates of mortality for both parasite strains; strain differences were also observed. The AR1 strain was significantly more resistant to copper toxicity than the AR5 strain in both high and low alkalinity waters. In general, these strain differences were more evident under conditions of low stress (i.e. low CuSO 4 concentration and high alkalinity), and suggest that genetic factors are overridden under high stress conditions. The present study establishes a role for alkalinity in the effectiveness of CuSO 4 treatment of ichthyophthiriasis and reveals differences in the susceptibility of parasite populations that are clearly important for control programs. KEY WORDS: Strain differences · Ichthyophthirius multifiliis · Copper toxicity Resale or republication not permitted without written consent of the publisherDis Aquat Org 83: [31][32][33][34][35][36] 2009 pounds at high alkalinities (Chakoumakos et al. 1979, Laurén & McDonald 1986. To account for this reduced toxicity or efficacy, the current practice for therapeutic use of CuSO 4 in culture ponds is to increase application rates in direct proportion to the total alkalinity of the water (MacMillan 1985, Tucker & Robinson 1990.It has become clear over the past decade that natural isolates of Ichthyophthirius multifiliis can be distinguished based on a number of criteria, most notably, the expression of surface immobilization antigens or i-antigens (Clark & Forney 2003). These antigens vary among natural isolates, and either monoclonal antibodies or reference polyclonal antisera that bind specific i-antigens can be used to define serotypes in simple immobilization assays (Dickerson et al. 1993, Swennes et al. 2006. Previous work has shown that serotype D strains are the most common in nature and express an abundant 55 kDa i-antigen on their surface (Wang et al. 2002). At least 5 additional serotypes of I. multifiliis have been identified based on antibodyspecific immobilization (Wang et al. 2002, Swennes et al. 2007, Xu et al. 2006 Swennes et al. (2007) has suggested that different strains of I. multifiliis vary with respect to virulence, and it would be reasonable to assume they differ in other phenotypic character traits as well.Previous research has investigated the effectiveness of CuSO 4 in controlling Ichthyophthirius multifiliis in several species of fish (Ling et al. 1993, Straus 1993, Schlenk et al. 1998, Tieman & Goodwin 2001, Goodwin & Straus 2006, Straus 2008, Rowland et al. 2009). The objective of the present study was to evaluate the acute toxicity of...

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